The present invention relates to image forming systems such as a color plain paper copy machine (hereinafter referred to as PPC) and a printer for printing/recording information from image information supply apparatuses such as a personal computer (hereinafter referred to as PC) and a digital camera on a plain paper, OHP sheet or other types of paper sheets, and particularly, it relates to a structure for holding an image holding member while a constant fine gap is always maintained on an abutment surface between a photosensitive drum or another image holding member and a developing roller.
An image forming system for use in the aforementioned purpose is provided with an image forming unit for forming an image by using a developing material, a sheet supply portion for supplying a sheet to the image forming unit, a sheet conveying portion for conveying the supplied sheet, and a sheet supplying/conveying controller for controlling the supplying/conveying of the sheet to the image forming unit by the sheet supplying and conveying portions. The image forming unit is provided with an image holding member for converting an optical image formed via an optical system into a latent image and subsequently depositing the developing material thereon to hold the image, a developing unit for developing the latent image held on the image holding member as the image with the developing material, a transferring unit for transferring the developed image to the sheet, and a fixing unit for fixing the transferred image.
In recent years, in a field of image forming system, various color developing/forming methods for forming color images have been proposed, and there are roughly a multiple transferring system and a multiple developing system. The multiple transferring system can be classified into a transferring drum system, a tandem system, an intermediate transferrer system, and the like, and the multiple developing system can be classified to a multiple rotation system and a one pass method. The transferring drum system comprises successively transferring respective color toners on a sheet wound around a transferring drum to obtain the image, and is characterized in that a positioning control is difficult but a degree of freedom in a process design is high. The tandem system is provided with image forming portions for four colors, successively transfers respective color toner images on a conveyed sheet to obtain the color image with one pass, and is high in cost and difficult in the positioning control, but is also provided with an advantage that image formation can be accelerated and a degree of freedom in process design is highest. The intermediate transferrer system comprises successively transferring respective color toner images on an intermediate transferrer, and subsequently collectively transferring the images to the sheet to obtain the color image, and is difficult in the positioning control and low in transfer ratio as compared with the other systems but has advantages that a transferring mechanism portion capacity is relatively small and that curvature separation is also possible.
Moreover, the multiple rotation system in the multiple developing system comprises rotating the photosensitive drum to superposing the respective color toners on the surface, and subsequently collectively transferring the toners to the sheet to obtain the color image, and requires a complicated process control, but is advantageous in miniaturization of a machine body and cost reduction, and has an advantage that the system is also advantageous for positioning. The one pass system is provided with the image forming portions for four colors around a photosensitive member, comprises superposing the toner images on the photosensitive member with one pass to obtain the color image, has difficulty in process arrangement around the photosensitive member and exposure positioning control, easily enlarges an apparatus size, and disadvantageously requires the complicated process control, but has an advantage that image formation can be performed at a high speed.
For the aforementioned image holding member for holding the image in an image forming process, in the aforementioned various image forming systems, concretely, there is one large-diameter photosensitive drum, or there are a plurality of relatively small-diameter photosensitive drums for respective colors in color copy or the like, but any member comprises a single photosensitive drum or a plurality of photosensitive drums as a constituting element of the image forming unit. The photosensitive drum is rotatably supported on a frame constituting a main body of the image forming system via a bearing or the like, and for the single photosensitive drum or the plurality of photosensitive drums a magnet roller for supplying the developing material is also disposed.
The developing magnet roller is disposed in parallel between a developing unit main body case and the photosensitive drum, and is used for attaching a toner as the developing material on an electrostatic pattern to form a visualized image after the electrostatic pattern is formed on the photosensitive drum charged with a static electricity by a charger in accordance with a document pattern by exposure by an optical unit. Therefore, by applying a bias potential of either a positive potential or a negative potential to the developing (magnet) roller to attach the developing material to the peripheral surface of the roller as an electromagnet and rotating the roller opposite to the photosensitive drum with a constant gap immediately before placing the roller in sliding contact with the peripheral surface of the drum, the toner is supplied to the surface of the rotating photosensitive drum which is charged in a predetermined document pattern and on which an electric latent image is formed.
As seen from the aforementioned description, since the photosensitive drum is disposed close to the developing roller to such an extent that the peripheral surfaces are nearly in the sliding contact with each other, a gap control is a big problem to secure an adequate supply amount of the developing material (toner). Particularly, in a recent technique it is a mainstream to integrally forming the photosensitive drum and developing (magnet) roller including the developing unit main body case, and it is very important to control the gap in arranging these components for every unit.
In the conventional image forming system, in order to control the gap between the peripheral surface of the photosensitive drum and the peripheral surface of the developing roller, an adjustment portion for the gap control is disposed in either edge of both ends avoiding a central portion for forming the image in the photosensitive drum, and a gap setting member fixed to a developing roller shaft is disposed opposite to the adjustment portion, and controlled by direct contact in such a manner that a constant distance is always held from the peripheral surface of the photosensitive drum (direct contact system). The gap setting member is provided with a disc shape or a thin cylindrical shape such that the peripheral surface abuts on the adjustment portion disposed on at least one edge of the peripheral surface of the photosensitive drum, and may be constituted, for example, by a bearing comprising an inner race fixed to the developing roller shaft and an outer race rotatably held via a plurality of rollers.
In the conventional image forming system constituted as described above, since the gap between the photosensitive drum and the developing roller is directly adjusted by the surface extended from the surface with the image to be formed thereon, distortion and rattling generated between a rotation drive shaft of the photosensitive drum and the rotation drive shaft of the developing roller, and disturbance forces such as cogging generated in a motor for rotating/driving both drive shafts are applied without being inhibited.
However, according to a conventional image forming device, collision of the peripheral surface of the photosensitive drum against the peripheral surface of the developing roller is avoided by the gap setting member coaxial with the developing roller and slightly larger in diameter than the developing roller, and the predetermined gap is always secured between the peripheral surface of the photosensitive drum and the peripheral surface of the developing roller, but a gap deviation between the peripheral surfaces of two rotating members is caused not by the peripheral surface itself, but by position deviations of the rotation shafts in two rotating members, and therefore the adjustment of the gap between both members by placing the gap setting member in sliding contact with the peripheral surface itself of the photosensitive drum cannot be said to be a direct way as a method of adjusting a gap fluctuation.
Moreover, the gap setting member is constituted by the bearing attached to the developing roller, and the outer race on the outer periphery of the gap setting member in sliding contact with the peripheral surface of the photosensitive drum is rotatable, but a part of the peripheral surface of the photosensitive drum is always in sliding contact with rotation in order to adjust the gap between both components, the peripheral surface edges are therefore worn, and as a result of long-time use a warp is generated between the peripheral surface on the center side of the photosensitive drum and the peripheral surface on the edge side in sliding contact with the gap setting member, which causes a problem that the gap between both components cannot accurately be adjusted.
Furthermore, for the position deviation of the peripheral surface between two rotating members having parallel rotation shafts, even when the gap adjustment is performed on one end side edge of the peripheral surface, with occurrence of a situation in which axial lines of the rotation shafts are not parallel to each other the constant gap can be maintained in the peripheral surface of one end side edge in sliding contact with the gap setting member, but the opposite peripheral surface in the other side edge is sometimes close to or apart from the predetermined gap, and it is difficult to maintain the predetermined gap over the entire area of the peripheral surface. To solve the problem it is also proposed to dispose the gap setting members on both ends of the developing roller, but even by a simple consideration two gap setting members are necessary, and the adjustment portion has to be also secured on the other edge opposite to the photosensitive drum, which therefore causes problems that manufacture cost increases and that a usable area of the photosensitive drum is narrowed.
The present invention has been developed to solve the aforementioned problems, and an object thereof is to provide an image forming system in which in order to adjust a gap between a photosensitive drum and a developing roller, instead of placing a gap setting member directly in sliding contact with a peripheral surface of the photosensitive drum, by allowing bearings of the photosensitive drum and developing roller to abut on each other to adjust the gap between both components in such a manner that a predetermined distance is maintained, gap adjustment is more precisely adjusted.
Another object is to provide an image forming system in which an accurate gap can be secured even after a long-time use without damaging the peripheral surface of the photosensitive drum in order to adjust the gap from the developing roller.
Further object of the present invention is to provide an image forming system which can accurately perform gap adjustment with respect the entire area of the peripheral surface without generating a gap fluctuation between both peripheral surfaces attributed to an axial line distortion or the like in two rotating members.
To achieve the aforementioned objects, according to a first basic constitution of the present invention there is provided an image forming system comprising: an image forming unit for forming an image by using a developing material; a medium supplying portion for supplying an image forming medium to the image forming unit; a medium conveying portion for conveying the supplied image forming medium; a medium supplying/conveying controller for controlling the supplying/conveying of the image forming medium to the image forming unit by the medium supplying portion and the medium conveying portion; a transferring portion for transferring the image developed by the image forming unit to the image forming medium; and a fixing portion for fixing the transferred image, wherein the image forming unit comprises: an image holding member for converting an optical image formed via an optical system into a latent image and subsequently depositing the developing material thereon to hold the image on an image holding surface, said image holding member being provided with a support shaft movably fixed to a main body frame of the system; a developing roller disposed in the developing portion for supplying the developing material to develop the latent image held on the image holding surface to the image with the developing material, and provided with a rotation drive shaft for supplying the developing material to the image holding surface; and a gap regulating mechanism which includes at least a first bearing for holding the support shaft of the image holding member, a gap setting portion, disposed at a predetermined distance from the first bearing in a direction of the image holding member, for holding the support shaft in the vicinity of the image holding member in an assisting manner, and a second bearing for rotatably holding the rotation drive shaft of the developing roller from the side of the developing portion and maintaining the distance between the image holding surface of the image holding member and the peripheral surface of the developing roller with the gap setting portion, and which sets a gap between two surfaces in such a manner that a constant fine gap is continued to be maintained between the gap setting portion and the second bearing.
In the image forming system according to the aforementioned first basic constitution, the gap regulating mechanism of the image forming unit according to a first middle constitution may be provided with: the first bearing and the gap setting portion laterally symmetrically disposed on both sides of the photosensitive drum as the image holding member; a coupling portion for coupling respective outer peripheral portions of the first bearing and gap setting portion; the second bearing having an outer peripheral surface opposite to the gap setting portion right close to both ends of the photosensitive drum via the outer periphery of the coupling portion and having its inner peripheral surface fitted into the rotation drive shaft of the developing roller; and an urging member for urging the developing roller in the direction of the image holding surface of the image holding member.
In the image forming system according to the first middle constitution, at least one of coupling members for coupling outer peripheral sides of the first bearing and the gap setting portion may be provided with a detail constitution by an elastic member for absorbing, by an elastic force, external action forces including deflection, distortion and eccentric action applied to the support shaft passed inside the diametric direction.
In the image forming system according to the detailed constitution, the elastic member may be formed of a thin member as compared with an ordinary coupling member, and elastically deformed to absorb the external action force when the external action force is applied around the support shaft to such an extent that the ordinary coupling member fails to be elastically deformed.
Moreover, in the image forming system according to the detailed constitution, the elastic member is constituted of a plurality of coupling pieces for bridging the first bearing and the gap setting portion, portions other than the plurality of coupling pieces are a plurality of openings which are lightened and opened, and the plurality of elastic pieces may be deformed to absorb the external action force when the external action force is applied around the support shaft to such an extent that the ordinary coupling member fails to be elastically deformed.
In the image forming system according to the first basic constitution, the gap regulating mechanism is provided with: the first bearing and the gap setting portion laterally symmetrically disposed on both sides of the photosensitive drum as the image holding member; a coupling portion for coupling respective outer peripheral portions of the first bearing and the gap setting portion; the second bearing having an outer peripheral surface opposite to the gap setting portion right close to both ends of the photosensitive drum via the outer periphery of the coupling portion and having its inner peripheral surface fitted into the rotation drive shaft of the developing roller; and an urging member for urging the developing roller in the direction of the image holding surface of the image holding member, and at least one of the first bearings may be formed by a positioning collar which is fitted into an attachment place of an image forming unit frame fixed on a main body side of the image forming system and which loosely supports the support shaft of the photosensitive drum inside the diametric direction to regulate a large displacement of the support shaft.
In the image forming system according to the first basic constitution, at least one of a pair of first bearings may be constituted by a bearing provided with an inner race into which the support shaft is fitted, an outer race which is fitted into the main body frame, and a ball sealed between the inner race and the outer race.
In the image forming system according to the first basic constitution, at least one of a pair of first bearings may be constituted by a sliding shaft bearing whose inner peripheral surface contacts the peripheral surface of the rotation drive shaft as the support shaft to support rotation of the rotation drive shaft.
In the image forming system according to the first basic constitution, at least one of a pair of gap setting portions may be constituted by a bearing provided with an inner race into which the support shaft is fitted, an outer race which is fitted into the main body frame, and a ball sealed between the inner race and the outer race.
In the image forming system according to the first basic constitution, at least one of the pair of gap setting portions may be constituted by a sliding shaft bearing whose inner peripheral surface contacts the peripheral surface of the rotation drive shaft as the support shaft to support rotation of the rotation drive shaft.
In the image forming system according to the first basic constitution, at least one of the pair of gap setting portions may be constituted by a fixing member, and one end of the fixing member abuts on the support shaft and the other end thereof abuts on the second bearing to set a gap between the image forming surface of the photosensitive drum supported by the support shaft and the outer surface of the developing roller.
In the image forming system according to the first basic constitution, the image forming unit is provided with a plurality of photosensitive drums as the image holding member, and a plurality of developing units as a developer for forming a pair with each of the photosensitive drums, at least the plurality of photosensitive drums are arranged in parallel in a tandem structure, and the plurality of photosensitive drums and a plurality of developing units may be assembled in one image forming unit case.
In the image forming system according to the first basic constitution, the image forming unit may have a transferring drum structure provided with a single photosensitive drum as the image holding member and a single developing roller as the developer.
In the image forming system according to the first basic constitution, the image forming unit may have an intermediate transferring structure provided with a single photosensitive drum as the image holding member, a plurality of developing rollers as the developer provided with different colors of developing materials disposed apart from one another via a predetermined angle around the photosensitive drum, and an intermediate transferrer for successively transferring the respective colors of developing materials formed on the photosensitive drum.
In the image forming system according to the first basic constitution, the image forming unit may have a multiple developing structure of one pass system which includes a single large-diameter photosensitive drum as the image holding member, and a plurality of developing rollers as the developer provided with different colors of developing materials apart from one another via a predetermined angle around the photosensitive drum, and which transfers a color image obtained by superposing the developing materials on the image holding surface of the photosensitive drum onto the sheet by passing the sheet as the image forming medium once to obtain the formed image.
In the image forming system according to the first basic constitution, the image forming unit may have a transferring drum structure which comprises at least a small-diameter rollershaped photosensitive member as the image holding member, a transferring drum provided with a large-diameter drum shape disposed on one side of the photosensitive member and the transferring portion on the peripheral surface of the drum shape, and a plurality of developing rollers for the respective developing materials disposed apart from one another via a constant angle on the peripheral surface of a large-diameter drum disposed on the other side of the photosensitive member, and which successively forms the images of the respective color developing materials on the image forming medium wound around the transferring drum to obtain a final color image.
In the image forming system according to the first basic constitution, the image forming unit may have a multiple rotation structure which comprises a large-diameter multiple-rotation photosensitive drum as the image holding member, and a plurality of developing rollers for the respective colors of developing materials disposed opposite to the image forming surface of the photosensitive drum and apart from one another by a predetermined angle, and which rotates the photosensitive drum multiple times to superpose the respective colors of developing materials on the image forming surface and then collectively transfers them to the image forming medium to obtain the color image.
According to a second basic constitution of the present invention there is provided an image forming system comprising: an image forming unit for forming an image by using a developing material; a medium supplying portion for supplying an image forming medium to the image forming unit; a medium conveying portion for conveying the supplied image forming medium; a medium supplying/conveying controller for controlling the supplying/conveying of the image forming medium to the image forming unit by the medium supplying portion and the medium conveying portion; a transferring portion for transferring the image developed by the image forming unit to the image forming medium; and a fixing portion for fixing the transferred image, wherein the image forming unit comprises: a photosensitive drum for converting an optical image formed via an optical system into a latent image and subsequently depositing the developing material thereon to hold the image on an image holding surface, said photosensitive drum being provided with a support shaft movably fixed to a main body frame of the system; a developing roller provided with a rotation drive shaft for supplying the developing material to the image holding surface to develop the latent image held on the image holding surface as the image by the developing material; and a gap regulating mechanism which includes at least first shaft holding means for holding the support shaft of the image holding member, gap setting means, disposed at a predetermined distance from the first shaft holding means in a direction of the image holding member, for holding the support shaft in the vicinity of the image holding member in an assisting manner, coupling means for coupling the first shaft holding means and an outer peripheral portion of the gap setting means, second shaft holding means for rotatably holding the rotation drive shaft of the developing roller from the side of the developing means and maintaining a distance between the image holding surface of the image holding member and the peripheral surface of the developing roller between the second shaft holding means itself and the gap setting means, said second shaft holding means being provided with an outer peripheral surface opposite to the gap setting means right close to both ends of the photosensitive drum via an outer periphery of the coupling means and an inner peripheral surface fitted into the rotation drive shaft of the developing roller, and urging means for urging the developing roller in the direction of the image holding surface of the image holding member, and which sets a gap between two surfaces in such a manner that the first shaft holding means and the gap setting means are laterally symmetrically disposed on both sides of the photosensitive drum and a constant fine gap continues to be maintained between the gap setting means and the second shaft holding means.
According to a third basic constitution of the present invention there is provided an image forming system comprising: image forming means for forming an image by using a developing material; medium supplying means for supplying an image forming medium to the image forming means; medium conveying means for conveying the supplied image forming medium; a medium supplying/conveying control means for controlling the supplying/conveying of the image forming medium to the image forming means by the medium supplying means and the image forming medium conveying means; transferring means for transferring the image developed by the image forming means to the image forming medium; and fixing means for fixing the transferred image, wherein the image forming means comprises: an image holding member for converting an optical image formed via an optical system into a latent image and subsequently depositing the developing material thereon to hold the image on an image holding surface, said image holding member being provided with a support shaft movably fixed to a main body frame of the system; a developing roller disposed in the developing means for supplying the developing material to develop the latent image held on the image holding surface to the image by the developing material, and provided with a rotation drive shaft for supplying the developing material to the image holding surface; and a gap regulating mechanism which includes at least first shaft holding means for holding the support shaft of the image holding member, gap setting means, disposed at a predetermined distance from the first shaft holding means in a direction of the image holding member, for holding the support shaft in the vicinity of the image holding member in an assisting manner, and second shaft holding means for rotatably holding the rotation drive shaft of the developing roller from the side of the developing means and maintaining the distance between the image holding surface of the image holding member and the peripheral surface of the developing roller with the gap setting means, and which sets a gap between two surfaces in such a manner that a constant fine gap continues to be maintained between the gap setting means and the second shaft holding means, the gap regulating mechanism comprises: coupling means for coupling the first shaft holding means and the gap setting means laterally symmetrically disposed on both sides of the photosensitive drum as the image holding member, and outer peripheral portions of the first shaft holding means and the gap setting means; the second shaft holding means provided with an outer peripheral surface opposite to the gap setting means right close to both ends of the photosensitive drum via an outer periphery of the coupling means and an inner peripheral surface fitted into the rotation drive shaft of the developing roller; and urging means for urging the developing roller in the direction of the image holding surface of the image holding member, and at least one of the first shaft holding means is formed by collar means which is fitted into an attachment place of the frame of the image forming unit fixed on a main body side of the image forming system and which loosely supports the support shaft of the photosensitive drum inside the diametric direction to position/regulate a large displacement alone of the support shaft.